How to make a loading bar work with a process - not time?
Scene loading

When a scene gets loaded the game will only do that and not refresh anything. The current (game) render will persist until the loading is completed.

Therefore your request will not do anything. You can't animate the render during loading.

LibLoad scene loading

You can load scene data from an external .blend file with LibLoad. The data will be merged into the current scene.

Synchronously

Per default it works like normal scene loading by showing the last render image until the load is complete = no animation.

Asynchronously

With the parameter async=True you can run the load over several frames.

The call provides you with a bge.types.KX_LibLoadStatus. From that you can read the current status of the load operation.

example [the code is untested]:

import bge

INTERNAL_PROPERTY_STATUS = "_internal.status"

def load(controller):
   '''Starts loading operation, stores the status in a property.'''
   status = bge.logic.LibLoad("demo.blend", "SCENE", async=False)
   controller.owner[INTERNAL_PROPERTY_STATUS] = status

def progressToValue(controller):
   '''Sets the value attribute of the first actuator to the progress from status.'''
   status = controller.owner.get(INTERNAL_PROPERTY_STATUS)
   if status == None:
      return

   actuator = controller.actuators[0]
   actuator.value = "'{}'".format(status.progress)
   controller.activate(actuator)


Be aware progress is a value from 0.0 to 0.1. You might want to scale it to your needs before using it.

Remark: I do not know if the progress shows more than 0.0 and 1.0 yet.